Steam & Excursion > Valves on an Air Pump?

How/what are the valves on an air pump. I assume there are separate valves for steam and air. what is the steam valve control mechanism?

Tominde Wrote:
-------------------------------------------------------
> How/what are the valves on an air pump. I assume
> there are separate valves for steam and air. what
> is the steam valve control mechanism?


As far as valves to operate the pump, there is a valve to turn the steam on and off and that is it. The air side of the compressor has chack valves that automatically control the intake, compression and exhaust of the ir.

Assuming you're talking about a typical Westinghouse 8 1/2" cross compound air pump, which I'll use for these illustrations. One cylinder pumps would be piped similarly, as would a New York air pump, except New York pumps put the steam cylinders on the bottom and the air cylinders on top.

Steam is supplied by a pipe to the boss "A". There us a valve in the cab on the turret supply this steam. It is considered an on/off valve, and is only used as a regulating valve when starting up the air pump. You don't want to run the pump full steam until air has been pumped up so the pump is working against a back pressure. There may be a second valve in the cab for this purpose. There may also be a valve in the steam supply pipe near the boss "A". A small petcock, "B", below the boss may be opened to bleed the steam when shutting down the pump.

Petcocks "C" at the bottom the high pressure cylinder and the low pressure cylinder are opened when starting up the pump to drain condensate and prevent damage from water locking. These are closed once the steel has warmed sufficiently to prevent condensation, and often have a wire handle dangling from them which can be reached from the ground.

There are no manually operated valves on the air cylinders.

All of the mechanism and valves to control the flow of live steam into the high pressure cylinder, between the high pressure and ow pressure cylinders, and exhaust are secreted away in the chambers "D" on top of the pump.

Exhaust steam is piped to the smokebox, or near the stack, by a pipe connected at boss "E" on the left side of the low pressure cylinder (hidden in this view).

Lubrication to the air cylinders is provided by oil cups to the left of "F". These will have petcocks to close when the engine is shut down for any extended period. These may be located as shown or lower, near petcock "C".

Lubrication to the steam cylinders can be handled one of two ways. First way is to install a hydrostatic lubricator in the cab. This forces steam oil into the steam supply pipe near "A". The second way is to install a small box called a mechanical lubricator near "A".

Lubrication of the piston rods is by clipping a swab onto the rods at "G". The swab is a C shaped metal band wrapped with wool soaked overnight in warm valve oil.

-John

---

Here's a pretty thorough article on cross-compound air compressors.

http://www.nelsonslocomotive.com/Heisler/Brakes/DesCompressor/DesCompressorI/DesCompressorI.htm

Hope this helps and doesn't make you too dizzy :-)

Have fun, be safe,
Bruce "Doc" Jones Sierra Madre CA

I neglected to mention there is also a governor in the steam supply line which regulates the steam to the compressor in responses to pressure changes in the main reservoir and to certain changes in the engineers use of the brake control valve.

-John



Edited 1 time(s). Last edit at 06/20/18 18:31 by LarryDoyle.

I’ll take a stab at this, Tom...

The cross compound pump, is my subject.
The top two cylinders are steam.
The two lower cylinders are the air compressor ....

The hi-pressure steam piston, the smaller one, drives the first stage of compressing the air.

So, the air leaving the low pressure piston is about 40-50 psi, is directed to the smaller-diameter air piston.
That small air piston is driven by the large diameter steam piston.

That low-pressure steam piston ( larger diameter) does not have its own reversing mechanism..... it responds to the “used steam “ ( compound). The LP steam piston pushes
the small diameter, high-pressure air piston which also benefits from the boost of air pressure coming from the low pressurecylinder
( about 50 psi) ....
The “staged” air AND steam combine to raise the compressed air pressure to about 150psi, to stuff into the main reservoirs...

The twice used steam is exhausted.

The heart of the ‘valve gear’ is the vertically positioned, ‘pilot’ valve directing the ‘reversing ‘ piston....
.( D, in the illustration, above)
The pilot valve is operated by a central cavity in H.P. stream piston rod.

The top cylinder head contains the reversing valves,
The LP piston configuration is simple; the piston rod only has the pistons on each end.

The H.P. piston rod is hollow about 2/3 of the way from the top... there is a small two-lobed piston valve that is moved at the top and bottom of the rod’s travel.
The small piston valve-rod has a long-tail drive rod, with a button at the bottom ( and a broad shoulder at the top, valve portion) extending into the hollow space in the rod.
( note: the hollow space in the rod is capped — with a key-hole opening—- to capture the button on the rod end—- thus, at the ends of the stroke, the button is nudged to its other position.. reversing the steam to the HP piston..).

The length of the ‘tail’ rod is just a little shorter than the travel of the HP piston.... thus, the reversing piston is lightly tapped at the end of each stroke, and moved to redirect the
boiler pressure steampath & stream
Is routed to the opposite ends of the Main Reversing valve...

The reversing pilot valve, shifts the live steam to alternating sides of the Main Reversing valve. ( F, in the illustration).

The Main Reversing valve is in a horizontal, large bore, valve bushing..... it moves to and fro, directed by the steam as sent by
( vertical) pilot valve...

The Main Reversing valve is a spool valve, with several lobes* to separate the steam paths of both the hi & low pressure steam...so that the machine makes two
strokes to compress the air...

So , to summarize, the hi- pressure steam piston travels end-to-end, being reversed at the very ends of each stroke...

That is the first stage of the two stage process..the “compound”,
lower pressure steam from the first cylinder, together with the boosted air pressure, assists , and is additive, to push-on their respective pistons to operate the H.P. ( air) cylinder ...forcing the 150psi air to the main reservoirs.

The valves in the air-end, the lower cylinders, are simple check valves that prevent back-flow of air (to the lower pressure). Each check valve operates independently.

As Larry Doyle pointed out, there is a pressure operated control valve that turns the compressors on —— when needed, and when the maximum air pressure is reached, the “automatic throttle-valve” shuts off the steam. That automatic valve is called, by Westinghouse, the compressor governor.,

When starting with no air in the main reservoirs , the ( air) high pressure piston barely moves...
The hollow rod and pilot valve of the HP ( steam) , do the reversing and slowly compresses the main reservoir air to about 50 psi....
While building to that tank pressure, the second piston rod barely moves...it’s waiting for the air pressure to combine with the compounded steam in order
to make its complete strokes...against the 150psi in the main reservoir..

When starting CC compressors, it’s vital that you open the steam valve gently...there is a slug of damaging water in the pipes supplying the compressor.
When all the water is drained from the steam cylinders, continue to operate the pump at a slow speed until about 50 pounds shows on the MR gauge in the cab.
Do NOT hurry this purposeful wam-up process.

Once, the minimum 50 psi pressure is reached, it’s ok to slowly, and fully, open the steam supply valve and let the compressor work at its natural speed.

The cross-compound compressor is a complex piece of equipment...
Become a student of its wonderful workings..

That was a great Question, Tom.

W.

* Note: early variants of the cross compound compressor used a multi-ported rectangular slide valve to control the steam flow paths... the improved versions use multi-lobed piston valves to redirect the steam...



Edited 8 time(s). Last edit at 06/20/18 03:54 by wcamp1472.

Gentlemen. I appreciated that you took time to type out these informative essays. That's not easy. You get an A in my book. I was having difficulty understanding how the reversing occurs in the HP steam. Man, I want to touch it and feel it again, now that you explained it.

Thanks much, Tom

OK, so we see that the governor controls the steam supply to the pump, supplying a maximum of 150 psi to the main reservoirs. I should also point out that there is a safety valve on the pipe at main reservoir No. 1, set to 165 psi. Everything described so far is, of course, assuming the engine is running properly and at near its normal maximum operating pressure.

Now, I'll throw this at you. What happens if, say, the fireman gets a severe case of clinker, can't restore his fire, and looses boiler pressure to operate the pump? (Wes, Jack, Bob K., 1522, Martin and other qualified engineers are disqualified from answering - or for 24 hours if no students figure it out.)

-John

Coal fire...

Instead of a clinker, suppose the fireman gets overzealous and shakes the grates hard enough that fire gets into the ashpan...then, that section of the grates burns-out, dropping melted grates into the pan..?

Resulting in loss of steam...

W...

AND....it’s not a double-header, and no dismals are doing the work ....



Edited 2 time(s). Last edit at 06/20/18 03:31 by wcamp1472.

Is this a trick question? I’m by no strech of the imagination an expert, but I *think* if boiler pressure dropped low enough to stop the compressor, the locomotive wouldn’t be moving very fast... unless downhill in a following wind...?

Go easy, folks, I’m old and brittle...!

Walter

Posted from iPhone

wcamp1472 Wrote:
-------------------------------------------------------
> Coal fire...
>
> Instead of a clinker, suppose the fireman gets
> overzealous and shakes the grates hard enough that
> fire gets into the ashpan...then, that section of
> the grates burns-out, dropping melted grates into
> the pan..?
>
> Resulting in loss of steam...
>
> W...
>
> AND....it’s not a double-header, and no dismals
> are doing the work ....


John and Wes,

Why is it always about coal? Back in 1977, on the Amtrak 4449 Transcontinental Steam Excursion, we cracked a boiler tube, enroute to New Orleans. The gradually increasing flow of water from the cracked tube, into the combustion chamber, and over the burner port, eventually put the flame/fire out. I will not continue with the rest of the details, until someone answers John's question about dropping steam pressure.

drumwrencher Wrote:
-------------------------------------------------------
> Is this a trick question? I’m by no strech of
> the imagination an expert, but I *think* if boiler
> pressure dropped low enough to stop the
> compressor, the locomotive wouldn’t be moving
> very fast... unless downhill in a following
> wind...?

No, there's no trick to the question.

A steam engine can still run at a pressure well below its rated pressure, it just runs less efficiently. To make up for lack of steam pressure the engineer will compensate by adjusting the Johnson bar to provide more steam to the cylinders in an effort to maintain speed. If the engine is designed for, say, 200 psi, it will take roughly 3 times as much water to maintain the same speed at 120 psi. Eventually, of course, the boiler will not be able to supply enough steam to maintain speed on level track.

But, for the sake of this discussion, let's say you are, indeed, going downhill with a tailwind, and the compressor does slow to a stop. Should he jump?

-John

HotWater Wrote:
-------------------------------------------------------
> John and Wes,
>
> Why is it always about coal? Back in 1977, on the
> Amtrak 4449 Transcontinental Steam Excursion, we
> cracked a boiler tube, enroute to New Orleans. The
> gradually increasing flow of water from the
> cracked tube, into the combustion chamber, and
> over the burner port, eventually put the
> flame/fire out. I will not continue with the rest
> of the details, until someone answers John's
> question about dropping steam pressure.

A) Because real firemen burn coal, and

B) I have 0 experience burning wood or oil.

-John <G>

One time, with intended light move from ( NKP 759), Baltimore to Hagerstown, a NKP safended flue separated—- before departing...

Details, later..

W.

Posted from iPhone

LarryDoyle Wrote:
-------------------------------------------------------
> HotWater Wrote:
> --------------------------------------------------
> -----
> > John and Wes,
> >
> > Why is it always about coal? Back in 1977, on
> the
> > Amtrak 4449 Transcontinental Steam Excursion,
> we
> > cracked a boiler tube, enroute to New Orleans.
> The
> > gradually increasing flow of water from the
> > cracked tube, into the combustion chamber, and
> > over the burner port, eventually put the
> > flame/fire out. I will not continue with the
> rest
> > of the details, until someone answers John's
> > question about dropping steam pressure.
>
> A) Because real firemen burn coal, and
>
> B) I have 0 experience burning wood or oil.
>
> -John

And the SP had successful coal burning cab forwards? Find it eazier to train an oil fireman on coal than a coal fireman on oil. Fewer rocks in the oil fireman's head and oil fireman are more in tune with what the locomotive is doing.


Dreamer



Edited 1 time(s). Last edit at 06/20/18 16:17 by Dreamer.

“....and oil fireman are more in
> tune with what the locomotive is doing.
>
>
> Dreamer...”


I challenge your comment about what the locomotive is currently doing...

Oil firing response times can be manipulated very quickly, if not instantaneously; but, it’s brutal on the boiler structure.
Oil fuel allows the fireman to react instantly ..... so. he can be a poor fireman....and keep the boiler pressure rock steady...at great cost...

Stoker equipped locos and Coal firing is much different...you're regulating the oxidizing process of the whole firebed...including the arch brick and the superheater...through the successful changes in firebed activity & overall boiler temperature
Changes to the temperature are necessarily more gradual, distributed better and makes for easier temperature swings on the firebox sheets.

Managing the coal fire means preparing the entire loco, well in advance, for the impending changes in demands.
If you wait to be in the middle of a firebox change-in-demand, or, when the track conditions are right under you, you’ve waited too long...

Thus, the crew of a coal-fired steamer, fireman and engineer, must work together, in a predictive manner, by about 3 to five minutes in advance of the anticipated & impending change in demands, to have a firebed ready -- well in advance--- for the upcoming challenges: up hill , or down hill, adverse signal aspects or expected stops, etc.

With coal, if you try to react by what’s in front of you, your firing attempts will lead to a shambles in the firebox.
Too much coal, too many bare spots, no rear bank for reserve, water too low, water too high, boiler pressure swings...all sorts of problems.
And, a grumpy engineer...

A good coal fireman can become an excellent oil fireman.
A good oil fireman, will take more time to adjust to coal’s burning patterns and tedious, firebox-delays & slow reaction times of coal-firing demands, as well as delayed reaction times of changes to the firebed's heat-generating conditions...

That's been my life experience and sad lessons..

W.



Edited 8 time(s). Last edit at 06/20/18 12:55 by wcamp1472.

wcamp1472 Wrote:
-------------------------------------------------------
> “....and oil fireman are more in
> > tune with what the locomotive is doing.
> >
> >
> > Dreamer...”
>
>
> I challenge your comment about what the locomotive
> is currently doing...
>
> Oil firing response times can be manipulated very
> quickly, if not instantaneously; but, it’s
> brutal on the boiler structure.

Not responding can be equally brutal If the draft is increased and the fire not increased accordingly the fire will be lost and the resulting temp drop will be dramatic where on a rock burner if there is a sufficient bed of coal you should have enough fuel to cover the increased draft and usage without an immediate response from the fireman. While the stocker engine, in either mechanical or biological form will need to increase the fuel input rate it does not necessarily change at the instant the locomotive throttle or valve settings are adjusted.

> Oil fuel allows the fireman to react instantly
> ..... so. he can be a poor fireman....and keep the
> boiler pressure rock steady...at great cost...

Poor fireman on an oil burner do not react instantly to the changing conditions, They can overreact and dirty the tubes with soot or not cover it completely and expose the firebox including tubes and tube sheets. to sudden contraction not seen with a coal burned due to the fuel bed. Remember even on a UP 4000 where 80 percent of the fuel was consumed in flight of the particle 20 percent still made it to the grate to cover such events.

>
> Stoker equipped locos and Coal firing is much
> different...you're regulating the oxidizing
> process of the whole firebed...including the arch
> brick and the superheater...through the changes in
> firebed activity & overall boiler temperature
> Changes to the temperature are necessarily more
> gradual, distributed better and makes for easier
> temperature swings on the firebox sheets.
>
> Managing the coal fire means preparing the entire
> loco for the impending changes in demands.

True, you can add more coal in anticipation where if you overfire with oil you can cut brick tubes and even protruding rivet heads or even worse. That is why oil burner fireboxes need to be inspected for metal conditions that are susceptible to flame cutting that a coal burner will tolerate more than oil.

> If you wait to be in the middle of a firebox
> change-in-demand, or, when the track conditions
> are under you, you’ve waited too long...
>
This not necessarily so. Having to high a water level is almost as bad as too low a water level. The damage to superheaters, pistons, and cylinder heads can be impressive. Understanding where your at on a railroad and where your going to need to be in the future is the mark of a good fireman of any fuel. sometimes you need to back off on the firing rate so you do not create trubble down the road..

> Thus, the crew, fireman and engineer, must work in
> a predictive manner, by about 3 to five minutes
> in advance of the impending change in seaman’s,
> to have a fire ready for the upcoming challenges,
> up hill , or down hill.

When firing on a railroad that many considered flat you could not set your self up 3 minutes before the Grade or grades. Infact midway during the trip we typically blew down and the level I bew down to depended upon my anticipated best average speed up the hill We would hit the bottom at 40 mph and if we were steam only we typically passed the worse of the grade at eight mph. If we had Diesel assist with 92 mph gearing we needed to be 12 mph at the same spot to avoid burning up traction motors. You had less time to put water into the boiler the faster you went so when you topped over at the top and started down a two percent grade without stopping a 30 mph you had enough water to cover the firebox.

>
> With coal, if you try to act by what’s in front
> of you, your firing attempts will lead to a
> shambles in the firebox.
> Too much coal, too many bare spots, no rear bank
> fir reserve, water too low, water too high, boiler
> pressure swings...all sorts of problems.
> An a grumpy engineer...
>
The advantage on hand fired coal burner with a grumpy engineer is you have a shovel. On an oil burner you only have a sand scoop to knock some sense into them. Bare spots can be a product of not setting up the proper coal beds. I needed to do a wide open throttle start on a coal burner due to conditions. My fireman had bought the extreme thin fire garbage from the CMO. When the engines draft was able to put holes in his fire it was because he was not preparing himself for possible conditions. Any locomotive slip would have done the same thing. Improper training can lead to increased maintenance needs on locomotives. Ironically this same RR had a book from when the locomotive was in regular service that said if the engineer was able to put holes in the fire the fireman need to increase the fire bed depth.

> A good coal fireman can become an excellent oil
> fireman.

True but because of their abilities not because of the fuel they use.

> A good oil fireman, will take more time to adjust
> to the coal’s burning patterns and tedious,
> firebed-delays of coal-firing demands...
>

No the fuels behavior will take time to learn but a good student will pick up on it quickly and if they keep a good bed to start with they will have time to recover. When a tourist RR went from Utah coal to the coal from the Hesperus mine in Colorado everyone noticed the Colorado coal took longer to ignite than the UTAH coal but it seemed to burn hotter and longer than the UTAH coal. If the increased energy consumption is not matched instantly in an oil burner you start disassembling the boiler faster due to more dramatic temperature changes The fire brick may hold a lot of heat due to its chemical composition but it only releases it at a certain rate.
When dealing with coal experienced engineers on an oil burner they typically did not communicate changes as well as experienced oil fired engineers. A good fireman knowing the route can only anticipate so much when dealing with an incommunicative engineer. That is why when I fired oil I like to sit at a 45 degree angle to the track so I can see ahead and the engineer. When training coal fireman they often asked me the difference and one day I had an engineer who ran oil at other places and to train the new fireman I asked him to act like we were on an oil burner. Two minutes later the student fireman was asking why he was saying so much.

> In my life experience and sad lessons..
>
> W.

All of the locomotive I have fired or ran were either hand fired or ex coal burners. The oil has been everything from used transformer oil (non PCB but with a fire retardant) to #6 with motor oil mixed in. Every fuel and every batch was different

My life experiences to this point

Dreamer



Edited 2 time(s). Last edit at 06/20/18 18:48 by Dreamer.

Back to the clinker fire going down hill.....

You still have air in the main tanks, but that has a very limited use. Can you run a cross compound on just the low pressure side to pump enough air?

Tominde Wrote:
-------------------------------------------------------
> Back to the clinker fire going down hill.....
>
> You still have air in the main tanks, but that has
> a very limited use. Can you run a cross compound
> on just the low pressure side to pump enough air?

No.

Well, so far nobody seems to want to answer John's question about what happens when steam pressure fails.